JP2002338980A - Lubricating oil composition and method for analyzing its deterioration - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thermally stable lubricating oil composition that has a low viscosity even at a low temperature and has a small viscosity change and small evaporation loss by using a base oil wherein a secondary ion intensity shows a peak at a position of a specified mass number as measured by a secondary ion mass spectrometry. SOLUTION: The lubricating oil composition comprises an ester-based base oil composed of a polyol and a fatty acid wherein a secondary ion intensity has a peak at least at the respective positions of mass numbers in one group selected from a first group consisting of mass numbers of 127, 213 and 357, a second group consisting of mass numbers of 141, 227 and 385 and a third group consisting of mass numbers of 155, 241 and 413 when the base oil is analyzed by a secondary ion mass spectrometer. Further, the lubricating oil composition comprises as an additive at least one of a hindered phenolic oxidant and a hindered amine antioxidant and additionally comprises a triglyceride as an additive.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lubricating oil composition (hereinafter, referred to as lubricating oil) for a hydrodynamic bearing used in a bearing portion of a rotating body such as a spindle motor.

[0002]

2. Description of the Related Art A device for rotating a disk such as a hard disk device for recording and reproducing data, or a motor for rotating a polygon mirror of a laser beam printer, not only requires a higher speed rotation but also improves the rotation accuracy and reduces the size. And low power consumption are required. For this reason, in spindle motors used for these, efforts have been made to replace bearings with hydrodynamic bearings in order to further improve rotational performance, reduce size, and reduce cost. In a hydrodynamic bearing, the characteristics of the lubricating oil, as well as the shape and precision of the hydrodynamic groove, greatly affect bearing performance including reliability.

[0003] That is, when the dynamic pressure is insufficient immediately after the start or stop of the spindle motor, boundary lubrication characteristics that suppress metal contact between the rotating shaft and the bearing are required. On the other hand, even when heat is generated during rotation during continuous operation, stable fluid lubrication characteristics with little deterioration such as oxidation, decomposition, and evaporation of lubricating oil are required. Further, in order to reduce the driving power of the motor, a low-viscosity lubricating oil having a small friction coefficient is also required.

Conventionally, lubricating oils used in hydrodynamic bearings include diesters such as DOS (di-2-ethylhexyl sebacate), which has excellent fluidity at low temperatures, and high viscosity and stability. There are triesters of trimethylolpropane and monovalent fatty acids.

[0005]

However, the above diesters and triesters have a viscosity at 40 ° C. of 1
0 to 30 mPa · s, 50 to 80 mP at 0 ° C
a · s, not only the viscosity is large but also the viscosity change with temperature is large. With such a viscosity, the friction of the lubricating oil itself becomes large, so that it is difficult to use a motor equipped with a hydrodynamic bearing in a device such as a portable device that emphasizes low power consumption. In addition, diesters are easily decomposed, while triesters have the property of polymerizing and increasing the viscosity when used for a long time. As described in the paper "Measurement of Bearing Temperature of Fluid Bearing Motors" published by the Japan Society of Mechanical Engineers (IIP 2001 Information, Intelligence, Precision Instruments Division Lectures, Lecture Papers, published by The Japan Society of Mechanical Engineers), the rotational speed of spindle motors It is reported that in a high-speed rotation region where the temperature exceeds 1.5 m / sec, heat generated by the coil of the motor portion is conducted to the bearing, and the temperature of the bearing portion exceeds 100 ° C. When a diester or triester is used under such a temperature condition, hydrolysis and polymerization of the lubricating oil composition are promoted, so that the hydrodynamic bearing is stably used for a long period of time under the above high-speed rotation conditions. I couldn't do that.

[0006]

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[0007]

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[0008]

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For example, a diester represented by DOS (di-2-ethylhexyl sebacate) generally has a structure represented by the following chemical formula (2). R4 and R shown here
5 represents a linear or branched alkyl group composed of CmHn (m and n are integers).

R4 and R5 have the same structure and CH ₂ CH ₂ R
In the case of a linear alkyl group consisting of, when exposed to high temperatures, the molecular motion of the base oil becomes intense, and the structure (Chemical Formula 2) easily changes to the structure of (Chemical Formula 3), and a pseudo bond of O—H Make 1 and 2. That is, the H atom 5 bonded to the C atom 3 or 4 in (Chemical Formula 3) with the given thermal energy,
When at least one of 6, 7, or 8 moves, a reaction as shown in (Formula 4) occurs and is relatively easily decomposed. In addition, (Chem. 4) shows the case where the H atom 5 or 7 shown in (Chem. 3) forms a transition state.
As described above, diesters in which R4 and R5 are linear alkyl groups have poor thermal stability.

At least one of the H atoms 5, 6, 7, or 8 bonded to the C atom 3 or 4 shown in Chemical formula 3 is a branched alkyl comprising a plurality of C atoms such as a methyl group or an ethyl group. When a group is used for R4 and R5, the reaction shown in (Formula 4) can be prevented by its steric inhibitory effect. However, when such a branched alkyl group is used, the viscosity of the lubricating oil increases. Therefore,
With diesters, it was difficult to satisfy both heat resistance and low viscosity.

As described above, the stability and viscosity of the lubricating oil are greatly restricted by the characteristics of the base oil, but it is difficult to easily evaluate whether or not the base oil has predetermined characteristics. .

An object of the present invention is to use a base oil having a secondary ion intensity peaking at a specific positive secondary ion mass per unit charge by secondary ion mass spectrometry, so that a low viscosity can be obtained even at a low temperature. It is another object of the present invention to provide a thermally stable lubricating oil having a small viscosity change and a small evaporation loss.

[0014]

The lubricating oil used in the hydrodynamic bearing of the present invention for solving the above-mentioned problems is an ester-based base oil comprising a polyol and a fatty acid. When analyzed by a secondary ion mass spectrometer,
The mass of positive secondary ions per unit charge is 127, 21
A first group of 3 and 357 values, 14
In one configuration selected from a second group consisting of values of 1, 227 and 385, and a third group consisting of values of 155, 241 and 413, at least the secondary ion intensity has a peak. However, in the secondary ion mass spectrometry, when the mass is M, the difference between adjacent masses obtained by measurement is ΔM, and the charge is Z, M
It is a value measured under static secondary ion mass spectrometry conditions where the mass resolution represented by / ΔM is 500 or less and under the condition where the mass is calibrated.

[0015] The lubricating oil contains at least one of a hindered phenol-based antioxidant and a hindered amine-based antioxidant as an additive. In the case of inhibitors, at least one (3,5-
Di-tert-butyl-4-hydroxyphenyl), and the total amount of this additive is at least 0.1% by weight or more. Further, the composition contains triglyceride as an additive.

By specifying the components of the base oil by static secondary ion mass spectrometry, a lubricating oil having low viscosity and high heat stability can be realized. In addition, the components of the base oil can be easily specified with a small amount and high accuracy. Furthermore, by adding a specific antioxidant or a specific component triglyceride as an additive to the base oil, a lubricating oil which does not decompose or oxidize even at a high temperature and has a small friction coefficient and good boundary lubrication is obtained. be able to.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The lubricating oil of the present invention is used for a hydrodynamic bearing which is filled between a rotating shaft and a bearing to generate dynamic pressure and support the rotating shaft in a non-contact manner. When the base oil is analyzed by a secondary ion mass spectrometer, the masses of positive secondary ions per unit charge are 127, 213, and 357.
, A second group of values of 141, 227, and 385, 155, 241,
And 413 in one group selected from the third group having the value of at least the secondary ion intensity. However, in secondary ion mass spectrometry, when the mass is M, the difference between adjacent masses obtained by measurement is ΔM, and the charge is Z, the static secondary mass resolution represented by M / ΔM is 500 or less. This is a value measured under ion mass spectrometry conditions and under conditions where the mass is calibrated.

By specifying the components of the base oil by static secondary ion mass spectrometry, a lubricating oil having low viscosity and high heat stability can be realized. In addition, the components of the base oil can be easily specified with a small amount and high accuracy.

[0019]

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That is, if a peak is obtained in the secondary ionic strength of each value of the first group to the third group, the structure of the base oil can be determined. For example, if a peak is obtained in the secondary ionic strength at a mass number of 127, 213, and 357 in the first group, the structure of the base oil as shown in (Chem. 5) can be specified. Note that R6
And R7 have the same structure when a peak is detected at the above mass number, and are a C ₇ H ₁₅ alkyl group. A peak corresponding to a mass number of 127 indicates that the portion represented by (a) was ionized in (Chemical Formula 5), and a peak corresponding to a mass number of 213 was ionized in a portion represented by (b). Indicates that The peak corresponding to the mass number of 357 indicates (S + H) ⁺ ionized by adding an H atom to the base oil molecule, where S is the mass of one base oil molecule. Therefore, by detecting peaks at the positions of the three mass numbers in the first group, the above-mentioned (Chemical Formula 5) and R6 and R7 become C
A base oil having a structure of ₇ H ₁₅ can be specified.

Similarly, in the case of the second group, if peaks are detected at three mass numbers, respectively, R
It can be specified that 6 and R7 are C ₈ H ₁₇ structures. In the case of the third group, if peaks are detected at three mass numbers, R6 and R7 become C ₉ H in (Chem. 5).
_It can be specified that the structure is ₁₉ .

Such a base oil hardly undergoes the reaction shown in Chemical formula 4, has good heat resistance, and has a viscosity of 40 ° C.
Is 12 mPa · s or less, and 48 mP · s or less at 0 ° C. Therefore, because of low viscosity, the coefficient of friction is small,
Energy loss in the bearing portion can be reduced, and it can be used under severe thermal conditions. The base oil may have at least a peak in the mass number of one group from the first group to the third group, and may have a peak in the mass number of another group. .

Further, the lubricating oil contains at least one of a hindered phenol-based antioxidant and a hindered amine-based antioxidant as an additive, and one of the additives is a hindered phenol-based antioxidant. In the case of inhibitors, at least one (3,5)
-Di-tert-butyl-4-hydroxyphenyl), and the total amount of the additives is at least 0.1% by weight or more. Note that (3,5-di-tert-butyl-4-hydroxyphenyl) may include at least one, and may include two, three, or four.

By adding a hindered phenol-based or hindered amine-based antioxidant to the ester-based base oil in an amount of 0.1% by weight or more, the lubricating oil is heated to a high temperature due to heating of the hydrodynamic bearing during high-speed rotation. In this case, deterioration of the characteristics of the lubricating oil can be prevented without oxidation. When the lubricating oil is exposed to high temperatures, it produces unstable peroxides as oxidation products formed initially. This decomposes to form new free radicals, which accelerates oxidation at an accelerated rate.Hindered phenol-based antioxidants or hindered amine-based antioxidants react with these free radicals to inactivate them. Therefore, oxidation can be prevented. Although the optimum amount of the antioxidant varies depending on the purpose of use, it is effective if at least 0.1% by weight or more is added. If the amount is too large, the performance of the base oil is deteriorated. Therefore, the upper limit of the amount is preferably 10% by weight, and more preferably 8% by weight or less almost deteriorates the performance of the base oil. More desirable as no range.

[0025]

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Further, the lubricating oil contains a triglyceride represented by the structure of Chemical Formula 6 as an additive. However, R1, R2 and R3 are each an unsaturated or saturated linear or branched structure composed of CxHyOz,
Further, R1, R2 and R3 have the same structure or at least one different structure, and the value of x is 15 to 2
1, the value of y is an integer value in the range of 29 to 43, and the value of z is in the range of 0 to 1. More specifically, when the value of z is 0, it is a structure of an unsaturated or saturated linear alkyl group or a branched alkyl group, and when the value of z is 1,
It has an OH group in the structure, and is an unsaturated or saturated linear or branched structure. When the structure has an OH group, the lubricity of the bearing member can be improved because the wettability of the bearing member with metal is improved. As for the values of x and y, when these values are increased, the triglyceride becomes solid and the compatibility with the base oil deteriorates, and the viscosity also increases. On the other hand, if the value is too small, the lubricating characteristics at the time of startup are deteriorated. Therefore, the above value is a desirable range as a condition for satisfying both.

Further, the total amount of the additives is 5% by weight or less. When the amount of triglyceride is increased, the performance of the base oil is reduced. However, the permissible limit of the performance when the triglyceride is added is 5% by weight. More desirable.

The triglyceride having the above structure is
By adding less than 10% by weight, the slidability in a metal contact state that occurs when the dynamic pressure decreases immediately after starting or immediately before stopping can be improved, so that the spindle motor is frequently started like a hard disk drive, Even in the case of a stop, friction and wear between the rotating shaft and the bearing portion can be reduced, and a highly reliable hydrodynamic bearing can be realized.

Further, the method for analyzing deterioration of lubricating oil according to the present invention is obtained by analyzing the initial state of a lubricating oil set and the lubricating oil used as a hydrodynamic bearing part for a certain period of time using a secondary ion mass spectrometer. Of the mass spectrum obtained, the secondary ionic strength at the position of the mass number in any one of the first group, the second group, and the third group is determined, and the secondary ionic strength of the used lubricant is determined. This is a method for evaluating a deteriorated state by obtaining a ratio between an ionic strength and a secondary ionic strength of a lubricating oil in an initial state.

Here, the static secondary ion mass spectrometry will be described. Secondary ion mass spectrometry is several to several tens keV
This is an analysis method for irradiating the surface of a sample with accelerated ions, called primary ions, which have been accelerated, and performing mass spectrometry on the generated secondary ions using a mass spectrometer, thereby identifying an element present in the sample. In static secondary ion mass spectrometry, the total amount of irradiated primary ions is set to 10 ¹² cm ⁻² or less. Then, the molecules present on the sample surface are generated as partial molecular ions, some of which are broken by the primary ions, and a mass spectrum is obtained which indicates the characteristics of the chemical bonds of the molecules present on the sample surface. In the present invention, a time-of-flight secondary ion mass spectrometry (time-of-flight second) using a time-of-flight mass spectrometer is used.
ry ion mass spectrometry:
TOF-SIMS) was used.

The TOF-SIMS uses the potential difference applied between the sample and the detector to fly generated secondary ions from the sample to the detector, and performs mass separation by detecting the secondary ions with the detector. . The mass of the monovalent ion is M and the velocity is V
Then, the energy E given to the ions by the potential difference is expressed by (Equation 1).

[0032]

(Equation 1)

The distance between the sample and the detector is L, and the time required for ions generated on the sample surface to reach the detector is t.
In this case, the speed V is represented by (Equation 2).

[0034]

(Equation 2)

(Equation 3) is derived from the above (Equation 1) and (Equation 2), and the mass of the ion can be measured by measuring the time required for the ion to reach the detector.

[0036]

(Equation 3)

From (Equation 3), ions having a small mass reach the detector early and are detected, and the amount of ions is monitored as the secondary ion intensity.

When the lubricating oil used in the hydrodynamic bearing is evaluated, the amount of oil used as the lubricating oil is as small as about several μL, but in TOF-SIMS, the amount of the The identification of existing elements and the analysis of organic molecules can be performed simultaneously. In addition, it is possible to analyze organic substances and inorganic impurities at one molecular layer level existing on the very surface with high sensitivity, and in particular, it is possible to analyze the state. Therefore, the deterioration of the lubricating oil composition base oil is analyzed by analyzing the intensity change of the mass spectrum. The analysis can be performed, and the identification of the metal element mixed in the lubricating oil composition and the analysis of the mixed amount can be performed. Note that the present invention relates to TOF-SI
It is needless to say that the present invention is not limited to MS, and that a general secondary ion mass spectrometer may be used.

A specific method for evaluating deterioration will be described.
In the spectrum obtained by performing secondary ion mass spectrometry on the lubricating oil in the initial state, the intensity of the secondary ion having a specific mass number is (I _R ) _{ref. n} ) _Ref . The intensities of secondary ions having the same mass number obtained in the used lubricating oil for a certain period of time and under a certain condition are respectively (I _R ) _after and (I _n ) _after
Then, the change rate IR (Int of the fragment of the lubricating oil)
(energy ratio) is expressed by (Equation 4).

[0040]

(Equation 4)

As the specific mass number and the mass number of interest, the first group consisting of the values 127, 213 and 357, the second group consisting of the values 141, 227 and 385, 155, 241, And 413, the secondary ion intensity of the mass number in one group selected from the third group. When the IR is 1, the fragment ion species of interest has not changed, indicating that the lubricant has not deteriorated. Also,
A value greater than 1 indicates that the ionic species is increasing, and a value less than 1 indicates that the ionic species is decreasing. In both cases, the larger the rate of change, the more the deterioration of the lubricating oil is advanced. Can be determined. As described above, the deterioration of the lubricating oil can be analyzed from the peak fluctuation of the fragment ion of interest.

[0042]

The present invention will be described below in detail with reference to examples.

Example 1 The lubricating oil of Example 1 was prepared as follows. The base oil, when analyzed using the secondary ion mass spectrometer described above, was of the first group, namely 1
At the positions of mass numbers of 27, 213, and 357, at least the secondary ion intensities respectively have peaks. The measurement conditions at this time are shown in (Table 1). C as primary ion
Using a ⁺ , the irradiation energy is 12 keV, the measured polarity of the secondary ion is positive, and the detection area is 40 μm ² . The measurement results are shown in FIG. 1, where (a), (b) and (S +
H) ⁺ is a peak corresponding to the fragment shown in (Chemical Formula 5), and its mass numbers are 127, 213, and 357, respectively. Further, as an additive for preventing oxidation of the base oil, four (3,5-di-tert-butyl-
1% by weight of a hindered phenolic antioxidant having (4-hydroxyphenyl) was added.

[0044]

[Table 1]

Example 2 The lubricating oil of Example 2 was as follows:
Adjusted as follows. Base oil uses a similar secondary ion mass spectrometer.
When analyzed using a second group, 14
At least at mass numbers of 1, 227 and 385
Each secondary ion intensity has a peak. This result
As shown in FIG. As in Example 1, (a), (b) and
(S + H) ⁺Corresponds to the fragment shown in (Chem. 5).
And their mass numbers are 141, 227,
And 385. In addition, to prevent oxidation of the base oil
4 (3,5-di-tert-butyl)
Hinderdov having tyl-4-hydroxyphenyl)
1% by weight of a phenolic antioxidant was added.

Example 3 The lubricating oil of Example 3 was as follows:
Adjusted as follows. Base oil uses a similar secondary ion mass spectrometer.
When analyzed with a third group, ie, 15
At least at mass numbers of 5, 241 and 413
Each secondary ion intensity has a peak. This result
As shown in FIG. As in Example 1, (a), (b) and
(S + H) ⁺Corresponds to the fragment shown in (Chem. 5).
And their mass numbers are 155, 241,
And 413. In addition, to prevent oxidation of the base oil
4 (3,5-di-tert-butyl)
Hinderdov having tyl-4-hydroxyphenyl)
1% by weight of a phenolic antioxidant was added.

Example 4 The lubricating oil of Example 4 was as follows:
Adjusted as follows. Base oil uses a similar secondary ion mass spectrometer.
When analyzed using a second group, 14
At least at mass numbers of 1, 227 and 385
Each secondary ion intensity has a peak. This result
As shown in FIG. As in Example 1, (a), (b) and
(S + H) ⁺Corresponds to the fragment shown in (Chem. 5).
And their mass numbers are 141, 227,
And 385. In the case of Example 4, the composition of the base oil
2 has the same structure as that of the second embodiment.
Can be found by comparing the results.

Further, as an additive for preventing oxidation of the base oil, four (3,5-di-tert-butyl-4)
-Hydroxyphenyl) was added in an amount of 1% by weight. In addition, 1% by weight of triglyceride represented by the formula (6) was added.
However, R1, R2 and R3 have the same structure, and CxH
It has a structure of yOz, the value of x is 17, the value of y is 33, z
Is 1.

(Comparative Example) DOS (di-2-ethylhexyl sebacate), which is a lubricating oil conventionally used for a hydrodynamic shaft, was used as a comparative example. FIG. 5 shows the spectrum of DOS measured by the mass spectrometer under the conditions described in Example 1.
Shown in The peak positions and their intensities are completely different from those of the ester base oils of Examples 1 to 4, and the differences can be clearly discriminated.

[0050]

[Table 2]

The main components of the lubricating oils of Examples 1 to 4 are shown in Table 2 below. (Table 2)
As can be seen, the main component amounts of the base oils of the lubricating oils of Examples 1 to 4 each have 85% or more.

With respect to the lubricating oils of Examples 1, 2, 3, 4 and the comparative example, viscosity, viscosity stability, evaporation amount, oxidation resistance, high-temperature stability, And the results of measuring the coefficient of friction are described below.

[0053]

[Table 3]

Table 3 shows the viscosities at 0 ° C. and 40 ° C. The lubricating oils of Examples 1 to 4 all had lower viscosities than the lubricating oils of Comparative Examples. When compared with specific numerical values, in Example 1, 48% at 0 ° C, 38% at 40 ° C,
In Example 2, 31% at 0 ° C., 26% at 40 ° C., Example 3
In Example 4, the viscosity was 11% at 0 ° C., 8% at 40 ° C., and in Example 4, the viscosity was 31% at 0 ° C. and 25% at 40 ° C. Therefore, compared to the lubricating oil of the comparative example that has been conventionally used,
The viscosity of the lubricating oil of this embodiment is small at both low and high temperatures, and therefore, the bearing loss of the hydrodynamic bearing can be reduced.

In order to maintain the rotation speed of the spindle motor with high accuracy, it is also important that the change in viscosity of the lubricating oil is small over a wide temperature range, and this change in viscosity was evaluated. As an evaluation method, the relationship between the viscosity Y and the reciprocal of the absolute temperature T is approximated by an exponential function represented by (Equation 5) using the viscosity data shown in (Table 3), and the viscosity change is determined by the value of the constant B. Compared.

[0056]

(Equation 5)

In (Equation 5), A and B are constants. The constant B indicates the slope of the curve, and indicates the rate of change in viscosity with respect to temperature. That is, the smaller the value of the constant B, the smaller the change in viscosity of the lubricating oil with respect to the temperature. The results are shown in Table 3 as B values. The B values of the lubricating oils of Examples 1 to 4 were clearly smaller than the B values of the lubricating oil of the comparative example, and it was found that the viscosity hardly fluctuated even with a temperature change.

A large change in viscosity means that the bearing loss increases on the low-temperature side where the viscosity increases, and that the lubricating oil film breaks on the high-temperature side where the viscosity decreases and seizure easily occurs due to metal contact. . Even when a device equipped with a motor using such a lubricating oil is used outdoors in winter or under a large temperature change condition such that the device is used after being left in a car in summer, the lubricating oil of the present embodiment has a viscosity change. Since it is smaller than the comparative example, the hydrodynamic bearing using these examples and the spindle motor using the hydrodynamic bearing have stable rotation performance even in a wide temperature range and in a high-speed rotation region. Obtainable.

Next, the measurement results of the evaporation loss will be described. Regarding the evaporation loss, the weight loss after leaving the lubricating oils of Examples 1 to 4 and the lubricating oil of the comparative example respectively in a thermostat at 100 ° C. for 120 hours was defined as the evaporation loss. It was determined in% by weight. The results are shown in Table 3 as the amount of evaporation. The evaporation loss of the lubricating oil of the present example was smaller than the evaporation loss of the comparative example as a whole, and in particular, the lubricating oil of Example 3 showed a significantly lower result. That is, since the lubricating oil of this embodiment has a small evaporation loss, even if it is operated for a long time, the lubricating oil does not run out, and the life of the spindle motor can be improved. In particular, the stability of the lubricating oil of Example 3 is remarkable.

Next, the heat stability when the lubricating oil was in contact with the rotating shaft and the metal as the bearing member for a long time in a high temperature state was evaluated by a high temperature acceleration test. The high-temperature acceleration test considers the state of the lubricating oil when the actual spindle motor is driven,
Using a heating oil bath with a shaker, the procedure was as follows. First, the lubricating oils of Examples 1 to 4 and the lubricating oil of Comparative Example were respectively poured into stainless steel test tubes. The same metal material as the rotating shaft and the bearing member was immersed in the lubricating oil in each of the test tubes into which the lubricating oil was injected. As the metal material, a material obtained by forming a nickel phosphorous plating film generally used for surface hardening on the surface of a cylindrical rod made of a copper alloy often used as a bearing member was used. These test tubes were immersed in a heated oil bath equipped with a shaker heated to 150 ° C. and vibrated to perform a high-temperature acceleration test. Because the shaker shakes the stainless steel test tube and the nickel-phosphorus-plated copper alloy rod in constant contact, a new surface is always formed on each metal surface, and the boundary lubrication condition can be realized.

As an evaluation method, a certain amount of each lubricating oil was sampled at every elapse of a certain period of time in the above-mentioned high-temperature acceleration test, the viscosity was measured, the evaluation was made based on the viscosity change, and the total acid number after 627 hours was passed. Was measured and evaluated. In the case of lubricating oils that have poor heat resistance, or that decompose or degrade using a metal as a catalyst, their viscosity changes due to the high temperature state or the catalytic action of the addition of a metal. Can be evaluated for heat resistance. In addition, the total acid value is an amount indicating, in milligrams, the amount of potassium hydroxide required to neutralize the acidic component contained in 1 g of the sample to be measured. When the value of the total acid number is large, it means that the lubricating oil is oxidized at a high temperature and further decomposes, and as a result, an acidic component is generated. Therefore, a lubricating oil having a large total acid number has a deterioration such as oxidation and decomposition, and the heat resistance can be evaluated.

FIG. 6 shows the results of measuring the change in viscosity in the high-temperature acceleration test. The horizontal axis shows the time maintained at high temperature,
The vertical axis shows the viscosity every elapse of a certain time. In addition, the measurement of the viscosity was performed at 40 degreeC. In the case of the lubricating oil of the comparative example, the viscosity increases almost linearly with the passage of time, and is substantially saturated when about 340 hours have passed. If the viscosity changes as described above, the bearing loss increases under use conditions in which the temperature of the bearing becomes high, so that it is difficult to use the bearing.

On the other hand, the lubricating oils of Examples 1 to 4
Almost no change in viscosity over time in the high-temperature acceleration test was observed, and it was confirmed that the heat resistance stability was remarkably good.

The results of measuring the total acid value of these lubricating oils after lapse of 627 hours are shown in Table 4. In all of the lubricating oils of Examples 1 to 4, the value of the total acid value was smaller than that of the comparative example, and it was confirmed that the heat resistance was good. In particular, in Examples 1 and 3, the value of the total oxidation number was 0, and decomposition was not caused even at a high temperature, and it was found to be a very stable lubricating oil. On the other hand, in the case of the lubricating oil of the comparative example, since the value of the total acid number is large, it can be seen that decomposition was caused by the high temperature acceleration test. That is, it was clarified that the lubricating oil of the comparative example had poor heat resistance stability and therefore had a large change in viscosity.

When the lubricating oil of Example 2 is compared with the lubricating oil of Example 4, the value of the total acid number of the lubricating oil of Example 4 is about 60 times that of the lubricating oil of Example 2. The results, which were smaller by%, showed that triglyceride also has an effect of suppressing the decomposition of the base oil.

[0066]

[Table 4]

The lubricating oils of Examples 1 to 4 in which the viscosity did not change in the nickel-phosphorus-plated copper alloy material were also subjected to a direct high-temperature acceleration test using the copper alloy material. The result is shown in FIG. The test conditions are the same as the above-mentioned high temperature acceleration test. As can be seen from the figure, it was clear that no change in viscosity occurred even when the copper alloy material was used, and it was found that the heat resistance stability was good.

However, as the metal material used for the rotating shaft and the bearing, not only the above-mentioned copper alloy or nickel-phosphorus-plated copper alloy but also various materials may be used. Depending on the requirements, an inhibitor for preventing metal corrosion or a metal deactivator may be added to the surface by coating such as plating or lubricating oil.

Next, the results of evaluating the sliding characteristics when metal contact occurs will be described. Metal contact occurs when the oil film breaks immediately after starting or stopping the motor on which the hydrodynamic bearing is mounted, and the coefficient of friction increases, resulting in large wear. This evaluation was performed by measuring the coefficient of friction using a pin-on-disk tester. In the pin-on-disk test, a stainless steel pin generally used for a rotating shaft and a copper alloy disk formed with a nickel phosphorus plating film which may be used in a bearing portion were used. As test conditions, the relative speed between the pin and the disk was set to 0.16 m / sec, and the load applied to the pin was set to 624 mN. The test results are shown in (Table 5).

[0070]

[Table 5]

In the case of the lubricating oils of Examples 1 to 4, at least a small coefficient of friction was obtained as compared with the lubricating oil of the comparative example. Among them, the lubricating oil of Example 4 had the lowest coefficient of friction, and the effect of adding triglyceride was clearly confirmed.

With respect to the lubricating oils of Examples 1 to 4,
The results of comparing the performance with the lubricating oil of the comparative example are summarized as follows.

That is, the lubricating oil of Example 1 has low viscosity and good heat resistance, but the evaporation amount is almost the same as the lubricating oil of Comparative Example. However, heat generation due to friction of the lubricating oil itself is small due to low viscosity, and therefore heat generation is suppressed as compared with the comparative example. Therefore, even if the evaporation amount is almost the same, it has higher temperature stability than the comparative example as a whole.

Examples 2 to 4 have good characteristics in all respects as compared with the comparative example, and show that they are lubricating oils having high heat resistance and small bearing loss.

As described above, the lubricating oil of this example had better overall characteristics than the comparative example, and a lubricating oil having high-temperature reliability could be realized.

The lubricating oil of the present invention may further contain various additives such as an oil agent, a metal corrosion inhibitor, or a metal deactivator according to the environment and conditions in which the hydrodynamic bearing is used. Is also good.

The lubricating oil of Example 1 has the lowest viscosity and excellent heat resistance. Therefore, for example, the fluid dynamic bearing of the motor for driving the rotating head drum of a camera-integrated video recorder or the spindle motor for mobile equipment is used. Suitable as a lubricating oil for use.

The lubricating oils of Examples 2 to 4 have better performance in all respects than the comparative examples, and are well-balanced lubricating oils. Since the lubricating oil of Example 4 has a smaller coefficient of friction, the motor is frequently started,
It is suitable for use to stop.

Further, the lubricating oil of Example 3 exhibits a viscosity close to that of the lubricating oil of the comparative example, but has a small evaporation loss, and is excellent in oxidation-decomposition resistance and heat resistance. It is suitable as a lubricating oil for a hydrodynamic bearing that requires high reliability and long life without deterioration.

(Embodiment 5) In this embodiment, the result of analyzing the deterioration using the lubricating oil described in Embodiment 2 will be described. That is, a start-stop test was performed at room temperature with a motor having a hydrodynamic bearing using the lubricating oil of Example 2.
Run for 00 hours. Tests were conducted on two types of motors, one having a bearing portion using a brass material which is a copper alloy containing zinc partially, and the other having a bearing portion in which the surface of the brass material was plated with nickel phosphorus. Lubricating oil after the test was collected, and its deterioration was analyzed by TOF-SIMS. The analysis conditions of TOF-SIMS are the same as those described in (Table 1).

In the spectrum obtained by the measurement, the secondary ion intensity of the (S + H) ⁺ peak where one molecule has an H atom, and the secondary ion intensity of the peak (b) obtained by the same measurement Ratio, IR _after = (S + H) ⁺ _after / (b)
I asked for _after . Also, similar ratios also lubricating oil before the _{test, IR ref. = (S +} H) + ref. / (B) ref. The calculated ratio of the IR _ref. And IR _after, i.e. IR _after
/ IR _ref. To evaluate the degree of deterioration. This value is shown in (Table 6). As can be seen from the table, in the case of the motor having the bearing portion plated with nickel phosphorus, it was recognized that the degree of deterioration was small, and the deterioration of the lubricating oil was large in the motor having the bearing portion using the brass material as it was. . (Table 6)
The metal components mixed into the lubricating oil analyzed at the same time
It is shown as a relative ratio to each component in the lubricating oil before the test. When the relative ratio is 1, it indicates that there is no change in the metal component in the lubricating oil before and after the test.
In the case of No., it is shown that it is 200 times larger than the lubricating oil before the test. When brass is used, Pb, which is an impurity component of the brass material, and Fe, which is a component of stainless steel that is a material of the bearing portion, are greatly increased in the same manner as Cu. It has been clarified that the lubricating oil also deteriorates due to the increase of the metal component.

[0082]

[Table 6]

By using the TOF-SIMS as described above, the deterioration of the lubricating oil used in the actual motor and the analysis of the mixed metal component can be performed. Furthermore, since the sample amount required for the measurement is as small as several μL, the deterioration of the lubricating oil can be analyzed accurately even in a bearing portion having a very small diameter.

In the present embodiment, the polarity of the secondary ion in the static secondary ion mass spectrometry is positive, but it may be negative. However, in this case, since the detected peak is different, a negative peak corresponding to a positive case may be used. In this embodiment, (S + H) ⁺ and (b) are used as the values of IR _after and IR _ref. , But the present invention is not limited thereto, and (a), (b) and (S + H) ⁺
Any combination of the ratios may be used.

[0085]

The lubricating oil used in the hydrodynamic bearing of the present invention for solving the above-mentioned problems is an ester base oil composed of a polyol and a fatty acid. When analyzed by an analyzer, the mass of positive secondary ions per unit charge was 127, 213, and 357.
, A second group of values of 141, 227, and 385, 155, 241,
And 413 have a peak in at least the secondary ion intensity in one of the groups selected from the third group.

The lubricating oil contains at least one of a hindered phenol-based antioxidant and a hindered amine-based antioxidant as an additive.
(3,5-di-tert-butyl-4-hydroxyphenyl). Further, the composition contains triglyceride as an additive.

By specifying the components of the base oil by static secondary ion mass spectrometry, a lubricating oil having low viscosity and high heat stability can be realized. In addition, the components of the base oil can be easily specified with a small amount and high accuracy. Furthermore, by adding a specific antioxidant or a specific component triglyceride as an additive to the base oil, a lubricant that does not decompose or oxidize even at high temperatures and has a small friction coefficient and good boundary lubrication is obtained. be able to.

Further, by determining the ratio of the mass spectrum by the secondary ion mass spectrometer before and after the use of the lubricating oil, the deterioration of the lubricating oil can be analyzed with a very small amount of sample with high accuracy.

[Brief description of the drawings]

FIG. 1 is a mass spectrum diagram of a lubricating oil of Example 1 of the present invention by secondary ion mass spectrometry.

FIG. 2 is a mass spectrum diagram of the lubricating oil of Example 2 of the present invention by secondary ion mass spectrometry.

FIG. 3 is a mass spectrum diagram of the lubricating oil of Example 3 of the present invention by secondary ion mass spectrometry.

FIG. 4 is a mass spectrum diagram of the lubricating oil of Example 4 of the present invention by secondary ion mass spectrometry.

FIG. 5 is a mass spectrum diagram of a lubricating oil of a comparative example of the present invention by secondary ion mass spectrometry.

FIG. 6 is a graph showing a change in viscosity of a lubricating oil according to Examples 1 to 4 of the present invention and a comparative example by a high-temperature acceleration test on a nickel-phosphorus-plated copper alloy.

FIG. 7 is a diagram showing a change in viscosity in Example 1 to Example 4 of the present invention by a high-temperature acceleration test for the same alloy.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G01N 23/225 G01N 23/225 33/30 33/30 // C10N 20:00 C10N 20:00 Z 30: 02 30:02 30:08 30:08 30:10 30:10 40:02 40:02 F term (reference) 2G001 AA05 BA06 CA05 DA01 EA04 GA02 KA12 LA04 MA02 4H104 BB05C BB34A BB34C BE07C DA06C EA21A LA01 LA04 LA05 PA01

Claims (8)

[Claims] 1. A base oil of a lubricating oil composition which is filled between a rotating shaft and a bearing to generate a dynamic pressure and is used for a dynamic pressure fluid bearing for supporting the rotating shaft in a non-contact manner, comprises a polyol and a fatty acid. A first group consisting of ester bases having a mass of positive secondary ions per unit charge of 127, 213, and 357 when the base oil is analyzed by a secondary ion mass spectrometer; , 227, and 385, a second group consisting of 155, 241, and 41
3. A lubricating oil composition having a peak in at least secondary ionic strength in one group selected from a third group having a value of 3. However, in secondary ion mass spectrometry, when the mass is M, the difference between adjacent masses obtained by measurement is ΔM, and the charge is Z, the static secondary mass resolution represented by M / ΔM is 500 or less. This is a value measured under ion mass spectrometry conditions and under conditions where the mass is calibrated. 2. At least one of a hindered phenol antioxidant and a hindered amine antioxidant
2. The method according to claim 1, wherein the seed is contained as an additive.
The lubricating oil composition according to the above. 3. The hindered phenolic antioxidant comprises at least one (3,5-di-tert) in the structure.
3. The lubricating oil composition according to claim 2, wherein the composition comprises (butyl-4-hydroxyphenyl). 4. The lubricating oil composition according to claim 2, wherein the additive contains at least 0.1% by weight or more. 5. The lubricating oil composition according to claim 1, comprising a triglyceride represented by the structure of Chemical Formula 1 as an additive. Embedded image Here, R1, R2, and R3 have an unsaturated or saturated linear or branched structure composed of CxHyOz. 6. R1, R2 and R3 of the triglyceride represented by the above formula (1) have the same structure or at least one different structure, and the value of x is 15 to 21, y
The lubricating oil composition according to claim 5, wherein the value of z is an integer ranging from 29 to 43 and the value of z is an integer ranging from 0 to 1. 7. The lubricating oil composition according to claim 6, wherein the amount of the additive is 5% by weight or less. 8. The secondary ion mass of the initial state of the lubricating oil composition according to any one of claims 1 to 7 and the lubricating oil composition used as a hydrodynamic bearing part for a certain period of time. Determining the secondary ion intensity at the position of the mass number in any one of the first group, the second group, and the third group of the mass spectrum obtained by analyzing with the analyzer; Lubricating oil characterized by evaluating the deterioration state of the lubricating oil composition by determining the ratio between the secondary ionic strength of the lubricating oil composition after and the secondary ionic strength of the lubricating oil composition in the initial state. A method for analyzing the deterioration of a composition.